|Publication number||US7280686 B2|
|Application number||US 10/447,599|
|Publication date||Oct 9, 2007|
|Filing date||May 29, 2003|
|Priority date||May 29, 2002|
|Also published as||CN1462016A, DE10224011A1, US20040008882|
|Publication number||10447599, 447599, US 7280686 B2, US 7280686B2, US-B2-7280686, US7280686 B2, US7280686B2|
|Inventors||Joachim Hornegger, Joachim Reiss, Christoph Schnoerr|
|Original Assignee||Siemens Aktiengesellschaft|
|Export Citation||BiBTeX, EndNote, RefMan|
|Patent Citations (30), Non-Patent Citations (1), Referenced by (9), Classifications (13), Legal Events (3)|
|External Links: USPTO, USPTO Assignment, Espacenet|
1. Field of the Invention
The present invention is directed to a computer-supported method for reconstructing an image of a three-dimensional subject, of the type wherein at least three two-dimensional projections of the subject, onto a projection surface composed of surface elements, that are offset from one another by difference angles are supplied to an evaluation computer, the difference angles being in a common rotational plane, the position in the projection surface and—per projection—a surface data value are respectively allocated to the surface elements, and volume data values for a number of volume elements to which respective positions in space are allocated are determined by the evaluation computer on the basis of the supplied, two-dimensional projections, so that the totality of volume elements represent a three-dimensional image of the subject.
2. Description of the Prior Art
Such methods are well known for C-arm X-ray systems. In such a system, the beam source and the projection surface are rotated synchronously and in the same direction through at least 180° and 44 through 400 X-ray exposures are thereby acquired. The reconstruction then ensues by means of the Feldkamp back-projection algorithm.
A rotation through by at least 180° is compulsory in the Feldkamp back-projection algorithm. The C-arm X-ray system that enables such a rotation through 180° and more, however, are relatively costly. There are therefore a number of systems wherein only rotation by an angle smaller than 180° is possible. A 3D reconstruction of the subject cannot ensue in such systems operating conventionally.
An object of the invention is to provide a computer-supported reconstruction method that enables a 3D reconstruction of the subject for a number of applications even when the beam source and the projection surface are rotated by an angle smaller than 180°.
This object is achieved by employing the volume data values that are binary.
Employing binary volume data values in fact represents an approximation, but the approximation is acceptable since high-contrast subjects are examined in many applications. In angiography, for example, the vessels of interest are filled with a contrast agent, or bones themselves already represent such high-contrast subjects.
The inventive reconstruction method, of course, can also be applied when a rotation by 180° or more ensues, but rotation by 180° or more is no longer compulsory. The sum of the difference angles thus also can be less than 180°. In particular, it is possible that it only amounts to 60 to 120°.
The projections preferably are uniformly distributed within the range of rotation with reference to the rotational axis. They can be parallel projections. Preferably, however, they are perspective projections.
Due to the simplified reconstruction method, it is now possible for the number of projections to be less than 40, particularly less than 20, for example less than 10. As a result of the inventive reconstruction method, it is possible to subject a patient to a notably lower radiation stress than in conventional reconstruction methods.
The volume data values represent a basic transparency and a minimum transparency of the subject. It is possible for the basic transparency and/or the minimum transparency to be determined by the evaluation computer together with the volume data values. Alternatively, of course, it is also possible to prescribe the basic transparency and/or the minimum transparency for the evaluation computer.
When the identified volume data values are stored in a bulk storage by the evaluation computer such that the volume data values of volume elements whose positions in space lie in a common plane are stored together, then an especially simple access to individual slices of the volume is achieved.
When the identified volume data values are stored in a bulk storage in DICOM format by the evaluation computer, the a widespread memory format is employed.
Due to the fact that the volume data values can assume only two different values, it is possible to first determine those volume data values that are sure to represent the basic transparency of the subject and to subsequently determine which values the remaining volume data values in fact assume, by testing the remaining possibilities (trial and error). It is simpler and faster, however, to use a method of discrete tomography for the determination of the volume data values.
As shown in
The imaging medical system further has a control and evaluation computer 5 that is connected to the beam source 1 and to the projection surface 2 in terms of control and data. The control and evaluation computer 5 is programmed with a computer program product 6 that determines the behavior of the control and evaluation computer 5. As a result of the programming with the computer program product 6, the control and evaluation computer 5 implements a reconstruction method for the subject 4 that is described in greater detail below.
The beam source 1 and the projection surface 2, as indicated by oppositely directed arrows at the beam source 1 and the projection surface 2 in
As can be seen from
As shown in
As can be seen especially clearly from
As shown in
It is assumed, the subject 4 is a high-contrast subject 4. For example, the subject 4 represents a vascular system filled with a contrast agent that is to be detected in an angiography procedure. Alternatively, the subject 4 can be composed of bone and the tissue surrounding the bones or bones. Each location of the high-contrast subject 4 therefore exhibits either a basic transparency t1 or a minimum transparency t2 dependent on whether the respective location lies in the highly absorbent or in the weakly absorbent region of the subject 4.
The subject is described by a number of volume elements 9 to each having a respective position xyz in space and volume data value vxyz are allocated. The volume data values vxyz are binary. When they assume the value zero, the corresponding volume elements 9 represent locations of the subject 4 that exhibit the basic transparency t1. When they assume the value one, they represent location of the subject 4 that exhibit the minimum transparency t2.
On the basis of the supplied, two-dimensional projections P, the volume data values vxyz for all volume elements 9 are determined by the control and evaluation computer 5 such that the totality of volume elements 9 represents a three-dimensional image of the subject 4.
The determination of the volume data values vxyz can ensue by determining at least the volume data values vxyz of those volume elements 9 that definitely exhibit the basic transparency t1. This will generally be the overwhelming portion of the volume elements 9. Due to the fact that the remaining volume elements 9 are thus already considerably reduced numerically and the volume data values vxyz are binary, i.e. can assume only two values, it is then possible with reasonable computing outlay to determine the volume data values vxyz of the remaining volume elements 9 by trial and error.
It is faster and more dependable, however, to determine the volume data values vxyz by means of a method of discrete tomography. Such methods are known, for example, from Kuba, Herman, Discrete Tomography, Birkhäuser Verlag 1999, and also can be applied without further ado in the present case.
It is possible to prescribe the basic transparency t1 and/or the minimum transparency t2 for the control and evaluation computer 5 either directly or indirectly. For example, a user can indicate what contrast agent is being employed in the angiography, so that the control and evaluation computer 5 can determine the corresponding transparencies t1, t2 on the basis of a table stored internally in the computer. Particularly in the application of the method of discrete tomography, it is alternatively possible for the control and evaluation computer 5 to itself determine the transparencies t1, t2 together with the volume data values vxyz.
After the determination of the volume data values vxyz, corresponding presentations of the subject 4 can be displayed on a viewing device 10. The determination of the presentations can thereby ensue in a known way, for example by means of the well-known volume rendering method. Alternatively or additionally, the volume data values vxyz can be stored in a bulk storage 11. The storage can ensue in arbitrary formats, but it preferably ensues in the DICOM format.
The volume data values vxyz preferably are stored in the bulk storage 11 so that the volume data values vxyz of volume elements 9 whose positions xyz in space lie in a common plane are stored together. This is indicated in
The inventive procedure shall be explained again based on
As indicated with broken lines in
The projection surface 2 is then irradiated through the subject 4 proceeding from the beam source 1 in a step 24. The projection P determined in this way is supplied to the control and evaluation computer 5 in a step 25. The index n is incremented by one in a step 26. A check to see whether the index n is greater than the plurality N is carried out in a step 27.
If the index n is not yet greater than the number N, then the beam source 1 and the projection surface 2 are rotated by the difference angle β (which is constant according to the exemplary embodiment) in a step 28. A branch is then made back to the step 24.
When, by contrast, the index n has reached the plurality N, then the control and evaluation computer 5 determines the volume data values vxyz on the basis of the surface data values fij of the projections P. As warranted, it also determines the transparencies t1, t2 in the step 29. The identified volume data values vxyz and the transparencies t1, t2 are stored in layers in the DICOM format in the bulk storage 11 in a step 30. Presentations of the reconstructed subject ensue on the viewing device 10 in a step 31.
Due to the limitation to high-contrast subjects 4, thus, three-dimensional reconstructions of the subject 4 are possible with the inventive reconstruction method even though only a very small number N of projections P was acquired and the rotational angle α is smaller than 180°.
Although modifications and changes may be suggested by those skilled in the art, it is the intention of the inventors to embody within the patent warranted hereon all changes and modifications as reasonably and properly come within the scope of their contribution to the art.
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|U.S. Classification||382/154, 345/419, 382/131, 600/428, 600/424, 600/431, 345/664, 382/285|
|International Classification||G06K9/00, G06T11/00|
|Cooperative Classification||G06T2211/436, G06T11/006|
|Sep 22, 2003||AS||Assignment|
Owner name: SIEMENS AKTIENGESELLSCHAFT, GERMANY
Free format text: ASSIGNMENT OF ASSIGNORS INTEREST;ASSIGNORS:HORNEGGER, JOACHIM;REISS, JOACHIM;SCHNOERR, CHRISTOPH;REEL/FRAME:014503/0385
Effective date: 20030603
|Mar 8, 2011||FPAY||Fee payment|
Year of fee payment: 4
|Mar 17, 2015||FPAY||Fee payment|
Year of fee payment: 8